Cytokeratin 7 and cytokeratin 20 expression in colorectal adenocarcinomas

Cytokeratin 7 (CK7) and cytokeratin 20 (CK20) are low molecular weight cytokeratins. The expressions of CK7 and CK20 have been studied in various primary and metastatic carcinomas. Their expression patterns may help to distinguish the site of origin of metastatic carcinomas. We investigated the expressions of CK7 and CK20 in 196 cases of colorectal carcinoma. Paraffin sections of 196 colonic adenocarcinomas were randomly selected, retrieved, and immunostained for CK7 and CK20 with a standard avidin-biotin complex method. CK7 was expressed in 34/196 (17.3%) and CK20 in 159/196 (81.1) cases of colorectal adenocarcinoma. CK7-/CK20+ had the greatest proportion (65.8%) in colorectal carcinomas. The CK7+/CK20+ immunophenotype was identified in 30/196 (15.3%), CK7-/CK20- in 33/196 (16.9%), and CK7+/CK20- in 4/196 (2%) colon adenocarcinomas. The CK7 and CK20 expression patterns were different in colorectal carcinomas according to histological grade, location of the tumor, and lymph node metastasis. CK20 positivity was more common in low grade carcinomas than in high grade carcinomas (85.1% versus 47.6%) and in rectal and sigmoid carcinomas than in proximal colon carcinomas (88.2% versus 63.2% and 88.9% versus 63.2%, respectively). Furthermore, CK7 expression was more common in tumors with lymph node metastasis than in non-metastatic tumors (25.3% versus 11%). In conclusion, a considerable number of colorectal carcinomas showed reactivity to CK7 (17.3%) or no reactivity to CK20 (18.9%). Therefore, CK7 positivity or CK20 negativity does not rule out a colorectal origin of metastatic carcinoma.